I have never sailed Princess but I would guess that if you have personal choice dining, a table for 2 shouldn't be hard to come by.
SJU is a growing AP. It is extremely over burdened on Sundays. Assuming you get there on time there is a VERY REAL possiblity that you will miss your flight b/c you can't get through TSA fast enough. They only have about 2 scanners for 5 cruise ships full of people. I have read posts about people making early flights with time to spare. What's your level of risk tolerance?
All depends upon what time your ship gets into port and is cleared for disembarkation. San Juan airport is a total zooey mess on Sundays! all the cruise ship passengers are doing the same thing you are, trying to get home. I seriously doubt that 11:50 am is doable. Seriously think about changing your flight.
It seems you've received a wide variety of opinions. I suppose you're just going to have to make a decision you feel meets your needs. I don't know if anyone has ever missed an 11:50 flight. I know that I have been to San Juan 3 times since the infamous 9/11, and I've always been at the airport by 10:20 AM for my flight out and I've always been at the gate waiting for my flight by 11:00 AM. Use your own judgement.
If you have an 11:50 flight out DO NOT take the ship's transfer. You will miss your plane for sure. Be one of the first off the ship, keep your fingers crossed & pray TSA is on it's toes that day. Assuming you make it to port on time, TSA will be your biggest hold up.
I agree that you should take a cab to the airport. There will be hundreds of cabs lined up to take people to the airport and it will be a 20 minute drive on Sunday morning and the cost is $20 plus tip. The only traffic will be at the port. Everyone else will be in church. San Juan is a very religious city. I still say you have nothing to worry about.